Electroslag refining apparatus

ABSTRACT

Electroslag refining apparatus comprises a mould having an upper open-end into which the lower end of an electrode depends and ducting to convey inert or reactive gaseous media to and from the mould. A device operable to restrict the flow of gaseous media is mounted on the upper end of the mould, and means are provided for effecting relative movement between the electrode and the flow restricting device. The flow restricting device includes a tubular, longitudinally-corrugated flexible member of heatresistant material which encompasses the electrode and which is so positioned and dimensioned that the apices of the corrugations make contact with the surface of the electrode over at least part of their lengths to define with the electrode surface discrete passages which inhibit the flow of air from the atmosphere to the upper portion of the mould. The arrangement is such that variations in electrode dimension and alignment relative to the mould are accommodated by flexing of the corrugated tubular member.

United States tet 1 t [111 3,777,041

Hawkins 1 Dec. 4, 1973 I ELECTROSLAG REFlNllNG APPARATUS v 'jPr imary E xaminer Roy N. Envall, [75] Inventor: Richard John Hawkins Kingston Atmmey-Le0 Rosetta Y UpomThames, England 7 ABSTRACT [73] Asslgnee: i f l E i kgsearch Electroslag refining apparatus comprises a mould havssoclahon on ng an 'ing an upper open-end into which the lower end of an [22] Filed: Mar. 22, 1973 electrode depends and ducting to convey inert or re- I active gaseous media to and from the mould. A device [211 App! 343379 operable to. restrict the flow of gaseous media is mounted on the upper end of the mould, and means [30] Foreign Application Priority D n; 1 are provided for effecting relative movement between Mar. 24 1972 Great Britain 13 885/72 the eleetrede and the new reemehhg deviee- The flew restricting device includes a tubular, longitudinally- 52 us. Cl. 13/17, 277/12 Corrugated flexible member of heat-resistant material 51 im. Cl. H05b 7/120 which emompahees the electrode and which is SO P [58] Field of Search ..13/14-17; honed and dimehsiehed that the aPieeS Ofthe corruga- 277/12 tions make contact with the surface of the electrode over at least part of their lengths to define with the [56] References Cited electrode surface discrete passages which inhibit the flow of air from the atmosphere to the upper portion UNITED STATES PATENTS of the mould. The arrangement is such that variations 1.SO8,486 9/1924 Tharaldsen 13 17'ux in elemode dimension and alignment relative to the 3:12: 5: mould are accommodated by flexing of the corrugated tubular member.

14 Claims, 5 Drawing Figures sir/7.041

PATENTED DEC 4 m5 SHEET 10F 2 FIG. 2.

PATENTEDUEC 4:915

SHEET 2 BF 2 FIG. 5. 7b

. E LIJCTRGSLAG REFINING APPARATUS This invention relates to electroslag' refining apparatus and'more especially to electroslag refining apparatus including means for restricting the flow of gas from a mould into which an electrode depends.

In the electroslag refining process, an electrically conductive slag within a mould is maintained in a mo]- ten state and at a temperature at or above the melting point of the metal to be refined. Unrefined metal is introduced into the mould and is refined as it passes in droplet form through a bath of the molten slag, refined droplets collecting to form a pool beneath the slag bath. The mould walls and baseplate are cooled by the circulation of a coolant, normally water, and a solidified ingot is built up beneath the molten metal pool. The metal to be refined may be introduced to the mould in the form of a consumable electrode which extends into the open-end of the mould, and the slag may be maintained molten by passage of an electric current from the electrode to the base plate of the mould.

For the manufacture of certain ingots, it is desirable that melting should be conducted in a controlled atmosphere, especially an oxygen-free atmosphere. Previously, oxygen-free atmospheres have been achieved by evacuating the upper portion of the mould. In processes such as electroslag refining in which a consumable electrode is moved downwardly relative to the mould during melting, sealing of the evacuated space has been found to be difficult and expensive.

According to the present invention, electroslag refining apparatus comprises a mould having an upper open-end into which the lower end of an electrode depends, means operable to convey gaseous media in communication with the mould, means for restricting the flow of gaseous media mounted on but insulated from the upper end of the mould, and means for effecting relative movement between the electrode and the flow restricting means, said flow restricting means including a tubular, longitudinal]y-corrugated flexible member of heat-resistant material which encompasses the electrode, the corrugated tubular member beingso positioned and dimensioned that the apicesof the corrugations make contact with the surface of the electrode over at least part of their lengths to define with the electrode surface discrete passages which inhibit the flow of air from the atmosphere to the upper portion of the mould and the arrangement being such that variations in electrode dimension and alignment relative to the mould are accommodated by flexing of the corrugated tubular member.

In the accompanying diagrammatic drawings FIG. 1 is a sectional elevational view of electroslag refining apparatus embodying the invention;

FIG. 2 is a perspective view of a flow restricting device illustrated in FIG. ll;

FIG. 3 is a cross-section taken along lines IIIIII of FIG. 2;

FIG. 4 is a detail of an alternative flow restricting device to that illustrated in FIGS. 1 to 3, and

FIG. 5 is a planview from above of further electroslag refining apparatus embodying the invention.

The apparatus illustrated in FIG. I includes an openended mould I mounted on but insulated from a cooled base plate 2. Ports 3, 4 are formed in the side wall of the mould l and communicate with ducting 5 intended to convey a gaseous medium, e.g. argon from a source 10, to and from the mould. A consumable electrode 6 of, for example, steel depends into the upper open-end of the mould 1 and a tubular flexible flow restricting hood member 7 is seated on the upper rim of the mould. The hood 7 is electrically insulated from the mould l and a seal 8 is positioned between the cooperating surfaces of the hood 7 and the mould l. The hood 7, which is shown in greater detail in FIGS. 2 and 3, comprises a lower ring-shaped member 9 (preferably of copper or steel) which seats upon the upper rim of the mould l and a longitudinally-corrugated tubular member 11 constructed of a material which can withstand the heat generated during operation of the apparatus and which will not contaminate the slag employed or ingot produced; the material may be, for example, metal such as copper or spring steel, plastics or ceramic material. The member 11 is secured by, for example, welding or clamping at its flared lower end to the member 9. The upper open-end of the member 11 is also flared to assist entry of the lower end of electrode 6 into the member 11. In its unflexed'configuration, the internal diameter of the member 11 is less than the diameter of the electrode 6. As shown in FIG. 3, the apices of the longitudinal corrugations of the tubular member 11 bear against the adjacent surface of the electrode 6 to define discrete passages which place the upper portion of the mould in communication with the atmosphere. The dimensions of the corrugations are such as to inhibit the flow of air from the atmosphere to the upper portion of the mould and to accommodate foreseeable variations in electrode diameter and misalignment of the electrode 6 relative to the mould l. The corrugations may either extend vertically or may be inclined to the vertical. One or more helical springs may be positioned about the outer surface of the corrugated member lll to urge the apices of the corrugations into contact with the surface of the electrode 6. Two such springs are indicated in broken line in FIG. 2 by reference numeral 12.

The electrode 6 is supported by a carriage 13 which is movable vertically along a mast 14 by means of a motor 15. The electrode'lfi and base plate 2 are connected into the secondary circuit of a transformer 16, the primary circuit of which is connected to a source of electrical current.

In operation, current is passed to the electrode 6 to maintain a bath of electrically-conductive refining slag 18 at a temperature at or above the melting point of the metal of the electrode 6 and droplets of unrefined metal pass from the electrode 6 and collect in a pool 19 below the slag bath 18. These droplets solidify to form an ingot 20. As the consumable electrode 6 melts and an ingot is built up below the metal pool 19, the electrode 6 is lowered by the carriage 13 at a controlled rate to maintain a pro-determined gap between the electrode tip and the surface of the metal pool 19.

For the melting of certain metals, it is desirable to prevent the flow of air from the atmosphere into the upper open-end of the mould to permit operation under a controlled atmosphere, especially an oxygenfree atmosphere. For such operation, an inert gas, e.g. argon or nitrogen, is conveyed to and from the mould space above the slag 18 through ducting 5 and ports 3, 4.

Prevention of an inflow of atmosphericair is effected by the apices of the corrugations of the member 11 pressing, due to their flexibility, against the opposed surface of the electrode 6. The flow rate of inert gas entering through port 3 and the pressure difference across the descrete passages defined between the member 11 and the electrode 6 are maintained at values such as to prevent the ingress of air from the atmosphere into the mould space and to prevent excess leakage of inert gas to the atmosphere. Variations in electrode thickness and misalignment of the electrode 6 relative to the mould l are accommodated by flexing of the corrugated member 11. I

Where added chemical reaction is required, the inert gas supplied via ducting may be replaced by a reactive gas. For example, a sulphur-containing gas may be supplied to control the sulphur level of the formed ingot 20.

FIG. 4 illustrates an alternative construction in which the ports 3, 4 of FIGS. 1 to 3 for conveying gaseous media to and from the mould are replaced by passages 21 formed in a flange member 22.v In this embodiment the lower end of the corrugated member 11 is urged against an upwardly standing flange 23 by means of a clamp 24.

In FIG. 5 there is illustrated an arrangement in which three consumable electrodes 6a, 6b, 6c of rectangular cross-section are refined simultaneously in a mould which is also rectangular in cross-section. The electrodes 6a, 6b, 6c are positioned in line along the longitudinal axis of the mould 1. As in the previously described ambodiment, each electrode is encompassed by a flexible longitudinally-corrugated hood member 7a, 7b, 7c, the apices of which bear against the adjacent surface of the respective electrodes. Preferably, the corners of each electrode are rounded and the corrugations are small compared with the radius of curvature of the rounded corners. The electrodes 6 extend through apertures formed in a plate 25 mounted on, but insulated from, the upper open-end-of the mould l and the hood members seat upon the plate 25. The electrodes may be connected one to each phase of a three-phase source of electricity.

The following is an example of a melt carried out using apparatus in accordance with the invention.

EXAMPLE A consumable electrode of mean diameter 127 mm was supported with its lower end depending into a mould of internal diameter 200 mm. The composition of the electrode was C 0.39; S 0.034; Si 0.20; Mn 0.80; Al 0.016; Ti 0.005; 0 32 30 parts per million.

A corrugated tubular copper hood member of diameter 120 mm in its unflexed mode was employed. The height of the member was approximately 70 mm and the length of each discrete passage defined between the opposed suffaces of the member and the electrode was approximately 50 mm, each passage being of approximately 3.5 mm in cross-sectional area. A slag of composition Ca F was employed.

Argon was supplied to the mould space above the slag bath at a flow rate of 10 litres per minute which was sufficient to give the minimum oxygen pressure as measured by an oxygen meter and this flow was maintained during remelting.

On completion of the melt, the argon supply was terminated, the hood removed and the ingot withdrawn from the mould.

The composition of the ingot was as follows: at the top of the ingot C 0.38; S 0.019; Si 0.18; Mn 0.74: A] 0.005; Ti 0.005; O l8, 17 parts per million.

At the base of the ingot": C 0.38; S 0.029; Si 0.18; Mn 0.77; -Al 0.005; Ti 0.005; 02 25, 26 parts per million.

Utilisation of the hood produced greater retention of sulphur and silicon and a marked reduction in oxygen content.

Whilst the invention has been described with reference to electrodes of circular and cylindrical crosssection, it is to be understood that corrugated flow restricting members in accordance with the invention may be employed with vessels into which electrodes of alternative cross-section, for example square or elliptical, depend, the flow restricting member being so shaped that the apices of the corrugations bear against the opposed surface of the electrode.

We claim:

1. Electroslag refining apparatus comprising a mould having an upper open-end into which the lower end of at least one electrode depends, means operable to convey gaseous media in communication with the mould, means for restricting the flow of gaseous media mounted on but insulated from the upper end of the mould, and means for effecting relative movement between the electrode and the flow restricting means, said flow restricting means including a tubular, longitudinally-corrugated flexible member of heat resistant material which encompasses the electrode, the corrugated tubular member being so positioned and dimensioned that the apices of the corrugations make contact with the surface of the electrode over at least part of their lengths to define with the electrode surface discrete passages which inhibit the flow of air from the atmosphere to the upper portion of the mould and the 1 arrangement being such that variations in electrode dimension and alignment relative to the mould are accommodated by flexing of the corrugated tubular member.

2. Apparatus according to claim 1 in which the means operable to convey gaseous media comprises a conduit which places the upper portion of the mould in communication with a source of inert gas.

3. Apparatus accordingto claim 2 in which the inert gas is argon. Y

4. Apparatus according to claim 1 in which the means operable to convey gaseous media comprises a conduit which places the upper portion of the mould in communication with a source of gas which reacts with the material to be refined.

5. Apparatus according to claim 1 wherein the longitudinally-corrugated member is secured at its lower end to a flange which is sealed on the rim of the upper open-end of the mould.

6. Apparatus according to claim 5 wherein the end of the conduit remote from the source of gaseous media communicates with the interior of the mould through a passage formed in the flange.

7. Apparatus according to claim 1 wherein means are provided to urge the apices of the corrugations into contact with the surface of the electrode.

8. Apparatus according to claim 7 wherein said means comprises at least one helical spring which encompasses the corrugated tubular member.

9. Apparatus according to claim 1 wherein a multiplicity of electrodes depend simultaneously into the least one electrode is circular in cross-section.

12. Apparatus according to claim 1 wherein said at least one electrode is rectangular in cross-section.

13. Apparatus according to Claim 9 wherein each of 5 said electrodes is circular in cross-section.

14. Apparatus according to Claim 9 wherein each of said electrodes is rectangular in cross-section. 

1. Electroslag refining apparatus comprising a mould having an upper open-end into which the lower end of at least one electrode depends, means operable to convey gaseous media in communication with the mould, means for restricting the flow of gaseous media mounted on but insulated from the upper end of the mould, and means for effecting relative movement between the electrode and the flow restricting means, said flow restricting means including a tubular, longitudinally-corrugated flexible member of heat resistant material which encompasses the electrode, the corrugated tubular member being so positioned and dimensioned that the apices of the corrugations make contact with the surface of the electrode over at least part of their lengths to define with the electrode surface discrete passages which inhibit the flow of air from the atmosphere to the upper portion of the mould and the arrangement being such that variations in electrode dimension and alignment relative to the mould are accommodated by flexing of the corrugated tubular member.
 2. Apparatus according to claim 1 in which the means operable to convey gaseous media comprises a conduit which places the upper portion of the mould in communication with a source of inert gas.
 3. Apparatus according to claim 2 in which the inert gas is argon.
 4. Apparatus according to claim 1 in which the means operable to convey gaseous media comprises a conduit which places the upper portion of the mould in communication with a source of gas which reacts with the material to be refined.
 5. Apparatus according to claim 1 wherein the longitudinally-corrugated member is secured at its lower end to a flange which is sealed on the rim of the upper open-end of the mould.
 6. Apparatus according to claim 5 wherein the end of the conduit remote from the source of gaseous media communicates with the interior of the mould through a passage formed in the flange.
 7. Apparatus according to claim 1 wherein means are provided to urge the apices of the corrugations into contact with the surface of the electrode.
 8. Apparatus according to claim 7 wherein said means comprises at least one helical spring which encompasses the corrugated tubular member.
 9. Apparatus according to claim 1 wherein a multiplicity of electrodes depend simultaneously into the upper open-end of the mould and wherein each electrode is encompassed by a said longitudinally-corrugated flexible member.
 10. Apparatus according to claim 9 wherein three electrodes depend into the upper open-end of the mould, the electrodes being connected one to each phase of a three-phase source of electric current.
 11. Apparatus according to claim 1 wherein said at least one electrode is circular in cross-section.
 12. Apparatus according to claim 1 wherein said at least one electrode is rectangular in cross-section.
 13. Apparatus according to Claim 9 wherein each of said electrodes is circular in cross-section.
 14. Apparatus according to Claim 9 wherein each of said electrodes is rectangular in cross-section. 